Paper-making machine



7 Aug. 25, 1931. I w. P.1'SCIHWEITZER 4 1,820,1 6 5- PAPER MAKING MACHINE Filed May 5, 1930 INVENITOR Wllr'ar/LBJMM ATTO Patented Aug. 25, 1931 UNITED STATES WILLIAM P. SCHWEITZER, OF HILLSIDE, NEW JERSEY PAPER-MAKING MACHINE Application filed May 3, 1930. Serial N0.449,404.

My present invention relates generally to paper manufacture, and has particular reference to an improved apparatus or machine for making paper of accurately uniform thickness.

It is a general object of my invention to provide a machine wherein an electrical apparatus, including current-indicating instruments or the like, may be employed in a practically automatic manner for ac curately measuring in a continuous and reliable manner the thickness of paper being manufactured, whereby the machine may be so regulated, either manually or automatically, that the output thereof will accurately uniform so far as thickness is concerned.

To illustrate the importance of accurate uniformity of thickness, I will state, by way of-example, that paper called for by manufacturers of paper dielectric condensers must comply with certain thickness requirements. For example, a condenser manufacturer may, in certain cases, call for and insist upon a .4 mil paper, and may in other cases specify a .5 mil paper. The former must be almost exactly .4 mil in thickness, and the latter .5 mil, because very slight variations in thickness areaccompanied by recognizable variations in dielectric properties.

A paper-making machine of the character to which my present invention has particular reference is the well known Fourdrinier machine wherein a mass of paper stock, consisting of finely comminuted pulp fibers and a liquid suspending medium therefor, is poured continuously upon a receiving end of a wire screen so as to form a web thereon. Usually, the liquid is water, and the machine not only forms but also advances the web in a continuous manner and treats the same, after its formation, to dehydrate it. The dehydration of water-removing procedure is accomplished in two parts, partly by mechanical dehydration means and partly by thermic means.

The reason why two procedures of dewatering or dehydration are required is that capability, and after the paper web has been bility of the mechanical dehydration mechain the advancement the mechanical apparatus is limited in itsfully squeezed and pressed it is necessary to remove the remaining entrained water by means of heat. 7

It has been found that the limit of capanism is of a definite character, dependent solely upon the type of pulp which is employed. In other words, if the stock fed to the web-forming wire is said to consist of (a) pulp, (1)) water entrained by the latter due to its intrinsic water-carrying capacity, and (a) a large amount of excess water, the mechanical apparatus for dehydrating the web is limited in its-capability to the excess water represented by (a) above. It makes no appreciable difference whether two press rolls or three press rolls are employed, and even if more press rolls or the like are employed, no appreciable additional water, beyond that represented by (c), would be expelled from the web.

This means that there is a critical point of the paper web, viz, after the mechanical dehydration has exhausted its capabilities, at which the amount .of waterstill entrained by the pulp bears V a definite ratio to the concentration of the latter, dependent only upon the characteristics of the pulp itself.

In accordance with my present invention, I resort to the electrical conductivity of the web at this critical point for obtaining a basis upon which to measure thickness or pulp concentration. For, since the pulp is practically non-conductive,the conductivity of a substantial web area at the critical stage is for all practical purposes directly proportional to the amount of water in such area, and since this amount of water bears a predetermined constant relationship to the amount of pulp in such area, the resistance variations serve as a basis for measuring variations inthickness.

I do not make any claim broadly to the utilization of the electrical-conductivity of the paper web. Devices have been previously provided wherein such electrical con ductivity isresorted to, but so far as I am aware n9 practical measurement or deter-,

mination of web thickness has ever been achieved.

I may state that the previous devices and machines which utilize the electrical conductivity of the web are, in my opinion, predicated upon assumptions which are either not Well founded or which result from an unthorough appreciation of the true nature and characteristics of the paper web and the effects upon it of the procedural steps'outlined herein. For example, I am aware of previous machines wherein the electrical conductivity is stated to be measureable anywhere along the web. This indicates a lack of appreciation of the critical stage previously mentioned and, so far as I can see, such electrical measurements can serve no useful purpose and are certainly unusable for determining and measuring web thickness. For, since the amount of water in a given web area before the critical stage is reached is an indeterminate and variable excess of the critical and constant percentage at the critical stage, the conductivity of such web area can bear no constant relationship to web thickness. And similarly, since the amount of water in a given web area after the critical stage has been passed is indeterminately and variably less than the critical percentage, the conductivity of such web area signifies if anything, only the op eration of the thermic dehydration apparatus.

I am also aware of prior attempts to utilize electric conductivity at isolated, relatively small areas of the web ostensibly to control the felts, pressure rollers, and other portions of the mechanical dehydration apparatus. But such measurements, showing the conductivity at isolated spots, do not indicate web thickness because the moisture variations at such spots may be due to the newness or condition of the felts and not to variations in pulp concentration.

I mention these previous devices to lay a basis for the statement that it is a feature of my present invention to utilize the electrical conductivity of a web area at the critical stage at which the water carried by the web bears a constant relationship to the amount of pulp in such area. And it is a second feature to utilize the conductivity of a substantial web area, e. g., an area which is coextensive in width with that of the web itself, so that variations in conductivity will serve as a basis for indicating minute-to-minute variations in pulp thickness throughout the entire width of the web.

A further feature of my invention lies in providing means for compensating the electrical-conductivity readings or measurements for possible variations that do not reflect web thickness but are due solely to variations in water purity. Here, too, I am aware of previous attempts to make comness remained constant. In the present instance, a maintenance of constant web thickness is the very object which my present invention seeks to achieve.

The apparatus which I provide consists essentially of a \Vheatstone-bridge electrical circuit. One resistance arm of the circuit is caused automatically to vary in direct proportion to the variations of resistance lengthwise through the substantial web area previously referred to. An adjacent arm of the bridge is caused automatically to vary in direct propostion to resistance variations perpendicularly through this web area. Any variations in water purity will affect both arms of the \Vheatstone-bridge circuit in the same proportion, and, as a result, the balance of the latter will be unaffected by such changes. On the other hand, as will be more fully understood after this specification has been read, variations in web thickness do not affect both of the foregoing resistance arms of the bridge in a compensating manner, but, quite to the contrary, in an opposite manner. Accordingly, by my apparatus, any unbalance of the bridge serves as an indication and a source of possible measurement of variations in web thickness, regardless of water purity.

My invention therefore enables me to uti-.

lize the readings of an electrical instrument for the purpose of indicating variations 1n thickness of the finished paper. Such variations may be due to fluctuating pulp concentration when the web is initially formed, or they may be due to fluctuations in speed of the mechanism for advancing the web. Obviously, if the pulp' concentration of the stock and the speed of movement of the web-forming apparatus could be accurately maintained uniform, the resultant paper would be accurately uniform in thickness. Unfortunately, however, it is practically impossible to control the pulp concentration to the required degree of accuracy, and accordingly, I provide means for controlling the speed of the web-forming and advancing apparatus as and when the results of the continuous electrical measurement or indication show that an adjustment is necessary.

For the attainment of the foregoing objects, I have provided an apparatus embodying the features of my invention and illustrated in the accompanying drawings, in which- Figure 1 is a diagrammatic elevational view of a typical paper-making machine, shown by way of example, and illustrating the initial formation of the paper web and wate'r'thus far effected by its advance up to and through the critical sta e hereinbefore referred to; and

igure 2 is a fragmentary perspective view of a portion of the present apparatus at said critical stage.

A continuously traveling wire screen 10 receives the mass of liquid stock 11 at a point 12. By assing under a doctor or slicer 13 the stoc consisting of paper pulp and water, is spread over a substantial width, thereby initially forming the web 14 upon the wire 10. A certain portion of the excess water is removed from the web during the advancement of the wire 10.

he wire passes'over a roll 15 which is arranged in close relationship to a roll 16. Passing beneath the'latter is a felt web or belt 17, and this felt is brought into contact with the aper web 14 as the latter passes between tlierolls 15 and 16. As a result of the comparative dryness of the felt 17, the web 14 is transferred bodily from the screen 10 onto the under-side of the felt 17 and is carried by the latter around the guide rollers 18 and 19.

The felt 17 then passes between the press rolls 20 and 21, and at this point the web 14 is brought into contact with a second felt 22. Due to the relative dryness of the latter, the web 14 is transferred to thefelt 22 and is carried by the upper surface thereof over the guide roller 23.

The felt 22 passes between the second set of press rollers 24 and 25 and in the machine herein illustrated no further felts are encountered, the web 14 being self-sustaining and traveling upwardly from the roller 25 as shown in the drawing. The felt 22 continues by itself over the guide roller 27 and eventually travels back to the first rollers 2021. Y

The self-sustaining web 14, upon leaving the roller pair 24-25, has arrived at the critical stage hereinbefore referred to. other words, .,-the mechanical expulsion of the several pressure rollers has exhausted its capabilities, and

the constituency of the self-sustaining web approaching the guide roller 26 consists solely of (aygpulp fibers, and (b) a predetermined amoiint'ofwater entrained by such fibers solely by virtue of their inherent water-carrying capacity. I have found this constituency to exist under normal day by day and week by week conditions, regardless of any special precautions or regulations relating to the fine adjustment of the efiiciencies of the several mechanical-explusion devices. In other words, assuming the machine to beoperating in its normally efiicient manner,- "I have found that the particular dryness or relative dryness of the felts, and the relative efliciencies of the pressure rollers, are immaterial so far as the constituency of the web 14 at the critical stage is concerned.

To measure an electrical more particularly, the electrlcal resistance, of a predetermined and constant area of sub stantial size of the web 14 at this critical stage, I cause the web to pass over a guide roller 29 having a metallic surface insulated from the rest of the machine. A contact 30 connects by a lead 38 with a source of electrical energy 31. The other terminal of the source 31 connects through a lead 39 with a point 40 at which two resistances hereafter to be referred to in greater detail are connected.

After passing over the roller 29, the web 14 is ready for the thermic treatment, which consists usually of several heated rollers of property, and,

the character typified by the first heat roll designated by the reference numeral 28. Eventually, the web 14 is wound upon a suitable mandrel or the like may not be subjected tocalendering treatment, etc.

In accordance with my invention, the predetermined and constant web area whose electrical resistance variations are utilized, consists of that rectangular area which is shown most clearly in Figure 2 and which extends between the dot and dash lines 36 and 37. The distance 35 between these lines remains constant because of the mounting and framework of the machine, the line 36 being the line of tangency between the web 14 and the roller 29, and the line 37 being the line of tangency between the web 14 and the roller 28. The lines 36 and 37 are parallel, are thus spaced by a fixed andconstant amount, and extend completely across the web between itsopposite side edges. Accordingly, if the tained constant, as it usually is, a constant rectangular web area of substantial size and coextensive in width with that of the web itself is subjected to the passage of an electrlc current, as will presently be described.

Before describing the operation of my apparatus, I will refer to the third electric terminal 41, which overlies the terminal constituted of the roller 29 but is positioned on the opposite side of the web. A contact 42 connects by a lead 43 to a point 44. Between the points 40 and 44 is a fixed resist- 'ance 45.

The thermic roller 28 is of metal and is electrically connected by meansof the lead 46 with the point 47. Between thepoints 40 and 47 I arrange a fixed resistance 48.

Between the polnts 44 and 47 I provide a and may or 45 and 48, and two other width of the web is main- 'adjacent resistance arms of which extend respectively from the points 44 and 47 to the point 51. In effect, I have inserted in the Wheatstone-bridge circuit, as one resistance arm thereof, the resistance of the.

the Wheatstone-bridge circuit, as an adjacent resistance arm thereof, the resistance of the web measured perpendicularly through the same between the terminals 29 and 41. The current-measuring instrument 50' will have a normal reading when the bridge is balanced, and whenever the bridge is unbalanced, the readings of the instrument 50 will serve as a measure of such unbalance.

The electrical effect of this arrangement is as follows. The instrument 50 being suit ably calibrated, and the resistances 45 and 48 being adjusted to make the instrument read its normal value, the balance will thereafter be maintained as long as the ratio of resistances between the point 51 and the points 44 and 47 respectively remains constant. This will be the case if the only changes in the paper Web are changes in water purity, because any such variations in water purity will afl'ect equally and proportionately the conductivity from the terminal 29 to the terminal 41, and from the terminal 29 to the terminal 28.

On the other hand, if web thickness should vary, the bridge would be thrown out of balance. This is due to the fact that one resistance path extends lengthwise through the web while the other resistance path extends perpendicularly through the web. For example, if the web thickness increases, the resistance lengthwise through the web from the terminal 29 to the terminal 28 will accordingly decrease. However, the increase in thickness will lengthen the path through which the current flows from the terminal 29 to the terminal 41, and as a result, this resistance measurement perpendicularly through the web will increase. This is the same electrical phenomenon which is recognized when a bar or wire of metal presents a decreased resistance to a lengthwise passage of current from point to point when the thickness of the bar or wire increases, while the resistance measured transversely through the bar or wire from point to point under such increase of thickness would increase because of the longer path.

A similar unbalance is created in the opposite direction if the web thickness decreases. The lengthwise resistance between the lines 36 and 37 would increase, while the perpendicular resistance between the terminals 29 and 41 would decrease.

In this way, it will be obvious that any currents likely to be induced in the circuit portion 49, and which are due solely to variations in water purity, are completely neutralized in an automatic manner so that the readings of the instrument 50 are unaffected by such variations in water purity. My present apparatus. and arrangement of parts assures me that the instrument serves without question as an indication of web thickness.

Accordingly, I am not only enabled to measure the thickness of the resultant paper in a continuous and automatic manner and without destroying the continuity of the web, but I am also enabled to control and maintain an accurately uniform thickness. I accomplish this last result by speeding up or retarding the wire 10 and the other parts of the machine. Suitable drive mechanism actuatcs the entire machine and, where the motive power is furnished by a steam engine, I have found it both simple and satisfactory to provide a speed-controlling mechanism which is operable upon the governor of the engine. The driving mechanism has not been illustrated'in the drawings because it would only serve to complicate the latter and because it is wellknown to those skilled in the'art. Usually, a system of gearing drives all the various portions of the machine, such as the wire screen and the press rolls. Nor have I illustrated the speed-controlling mechanism, which may be of any suitable character. I may mention that I have satisfactorily employed a manual control such as a hand wheel preferably positioned close to the instrument 50 and serving to adjust the governor of the steam-engine of similarly to vary the motive power.

In practice, I prefer to calibrate the meter 50 so that it will read Thickness of paper produced, but this is not essential because it can easily be learned from experience that a certain particular reading must be maintained in order to maintain a certain corresponding thickness of resultant paper. For example, should the pointer of the instrument 50 swing in one direction, it would be an indication that the amount of pulp distributed over the constant web area had increased; whereas if the pointer should swing in the opposite direction, it would be an equally sure indication that the amount of pulpdistributed over the same area had diminished. In the latter case, for instance, the speed of the wire 10 would be slowed up by a sli 'ht amount, thereby promptly and effectively restoring the proper and desired pulp distribution per length of web. In like manner, the wire 10 would be speeded up by a slight amount whenever the unbalance of the \Vheatstone-bridge circuit indicated that the pulp concentration had increased.

I am not concerned with the accurate efiiciency of the heat rolls any more than I edges. Such variations may,

provide only a single point am with the accurate control of the mechani:

cal dehydration mechanism. So long as such heat treatment is maintained normally efli cient in accordance with customary practice and operation, the resultant paper will meet even the accurate requirements of such users thereof as condenser manufacturers.

Similarly, since I measure across the entire width of the web at all times, .I am not concerned with variations in web thickness transversely of the web between its opposite perhaps, be due from time to time to improper or worn crowning of the rollers, or to wear of the felts, but such variations in the rollers or felts occur at comparatively rare times and can be gradually anticipated as the respective parts remain in use for known periods of time. In other words, there are no minute-to-minute variations transversely of the web as there are minute-to-minute variations in weight distribution of pulp and web thickness.

In general, I wish to emphasize again that the minute-to-minute variations in web thickness are the only ones (except those due to variations in water purity), which have any true significance and which affect the resistance of the substantial web area I have shown. Since the variations in the purity of the water are eliminated as factors by my present apparatus, I am enabled to derive beneficial and highly useful indications from the instrument 50.

It will be understood that although I have shown the terminal 41 as a roller similar to the roller 29, nevertheless I need not employ such a terminal but may, if convenient,

contact, or several of them. The essential thing is that the resistance ofthe web be measured perpendicularly through the web. Similarly, I need not necessarily employ the terminal 29 as a common terminal, but it would be equally feasible under certain conditions to provide a total of four terminals, two of which would measure the resistance lengthwise through the web while the other two would measure the resistance perpendicularly through the web.

Of course, whatever form the two terminals may take which measure the resistance perpendicularly through the web, one or the other, or both, must .be yieldably mounted to provide for the possible increase or decrease in web thickness as the pulp concentration increases or decreases.

It will also be understood that wherever I I have used the term lengthwise through the web herein, or in the appended claims, I do not necessarily referto a measurement in a direction parallel to the web travel. The essential thing is that this resistance measurement be made longitudinally through the web for a predetermined and whereby the extent vention may be made by those skilled in the art without departing from the spirit and scope of the invention as expressed in the appended claims. It is therefore intended that these details be interpreted; as illustrative, and not in a limiting sense.

Having thus described my invention and illustrated its use, what 1 claim as new and desire to secure by Letters Patent is 1. In a paper-making machine, means for continuously forming and advancing a paper web composed of pulp and water; a Wheatstone-bridge electric circuit; and means for automatically varying the resistance of one bridge arm in proportion to resistance variations lengthwise through a constant web area, and for automatically varying the resistance of an adjacent bridge arm in proportion to resistance variations perpendicularly through said web; whereby the balance of said bridge will be unalfected by variations of water purity, and whereby the extent of unbalance will serve as a measure of variations of web thickness in said area;

2. In a paper-making machine, means for continuously forming and advancing a paper web composed of Wheatstone-bridge electric circuit; and means for automatically varying the resistance of one bridge arm in proportion to resistance variations lengthwise through a constant web area which is dehydrated to the limit of capability of said mechanical means, and for automatically varying the resistance of an adjacent bridge arm in roportion to resistance variations perpen icus pulp and water; mechanlcal means for dehydrating said web; a-

varying the resistance of an adjacent bridge arm in proportion to resistance variations perpendicularly through said web area; whereby the balance of said bridge will be unalfected by variations, of water purity, of unbalance will serve as a measure of variations of web thickness in said area.

4. In a paper-making machine, means for continuously forming and advancing a paper web composed of pulp and water;

mechanical means for dehydrating said web to expel excess water; a Wheatstone-bridge electric circuit; means for inserting into said circuit as one arm thereof the lengthwise resistance through a constant web area which is dehydrated to the limit of capabils ity of said mechanical means; and means for automatically varying the resistance of an adjacent bridge arm in proportion to resistance variations perpendicularly through said web area; whereby the balance of said bridge will be unaffected by variations of water purity, and whereby the extent of unbalance will serve as a measure of variations of web thickness in said area.

5. 'In a paper-making machine, means for continuously forming and advancing a paper web composed of pulp and water, an

electrical circuit including a portion with a current-responsive instrument therein,

means for automatically making the current variations in said circuit portion responsive to resistance variations measured in two per endicular directions through a constant we area, and means'for neutralizing any current variations in said circuit portion which are due solely to variations in water purity, whereby said instrument will be indicative of web thickness in said area regardless of the purity of the water therein.

6. In a paper-making machine, means vfor continuously forming and advancing a paper web composed of pulp and water; an electric terminal extending transversely across the web and in contact therewith, a second electric terminal fixedly spaced from the first terminal and extending transversely across the web and in contact therewith; a third electric terminal overlying the second terminal and contacting with the opposite surface of the web; a Wheatstonebridge electric circuit; and means for automatically varying the resistance of one bridge arm in proportion to resistance variations of the web between said first and second terminals, and for automatically varying the resistance of an adjacent bridge arm in proportion to resistance variations of the web between said second and third terminals.

7. In a paper-making machine, means for continuously forming and advancing a paper web composed of pulp and water; an electric terminal extending transversely across the web and in contact therewith, a second electric terminal fixedly spaced from the first terminal and extending transversely across the web and in contact therewith; a third electric terminal overlying the second terminal and contacting with the o o site surface of the web; a Wheatstone-bndge electric circuit; means for inserting into said circuit as one arm thereof the web resistance between said first and second terminals,

and means for automatically varying the resistance of an adjacent bridge arm in proportion to resistance variations of the web between said second and third terminals. v

8. In a paper-making machine, means for continuously forming and advancing a paper web composed of pulp and water; an electric terminal extending transversely across the web and in contact therewith, a second electric terminal fixedly spaced from the first terminal and extending transversely across the web and in contact therewith; a third electric terminal overlying the second terminal and contacting with the opposite surface of the web; a Wheatstone-bridge electric circuit; and means for automatically varying the resistance of one bridge arm in proportion to resistance variations of the web between said first and second terminals, and means for inserting into said circuit as an adjacent arm thereof the web resistance between said second and third terminals.

9. In a paper-making machine, means for continuously forming and advancing a paper web composed of pulp and water; an electric terminal extending transversely across the web and in contact therewith, a second electric terminal fixedly spaced from the first terminal and extending transversely across the web and in contact therewith; a third electric terminal overlying the second terminal and contacting with the opposite surface of the web; a Wheatstonebridge electric circuit; means for inserting into said circuit as one arm thereof the web resistance between said first and second terminals, and means for inserting into said circuit as an adjacent arm thereof the web resistance between said second and third terminals.

10. In a paper-making machine, means for continuously forming and advancing a paper web composed of pulp and water; a pair of electric terminals contacting with the web along spaced lines of contact so as to pass acurrent lengthwise through the web, a pair of juxtaposed electric terminals contacting with the web on opposite sides thereof so as to pass a current perpendicularly through the web, a Wheatstone-bridge electric circuit, and means for passing said lengthwise and perpendicular currents through two adjacent arms of said bridge, respectively.

11. In a paper-making machine, means for continuously forming and advancing a paper web composed .of pulp and water; means for measuring the electrical resistance of the web perpendicularly therethrough, means for simultaneously measuring the electrical resistance of the web lengthwise therethrough and through a fixed distance, and means for continuously-utilizing said resistances as two adjacent resistance arms of a Wheatstone-bridge.

12. In a process of paper manufacture wherein a paper web of pulp and water is continuously formed and advanced, the herein-described step or steps of controlling the arms! of a Wheatstone-bridge,

thickness of the web by electric resistance measurements, which procedure consists in passing an electric current lengthwise through a constant web area and also perpendicularly through said web, whereby said currents will vary as the resistances of their paths through the web vary, and causing said currents conjointly to influence an electric-measuring instrument.

13. In a process of paper manufacture wherein a paper web of pulp and water is continuously formed and advanced, theherein-described step or steps of controlling the thickness of the ance measurements, which procedure consists in passing an electric current lengthwise through a constant web area and also perpendicularly through said web, whereby said currents will vary as the resistances of their paths through the web vary, and registering on an electric-measuring instrument the effect of only those current variations which are not directly proportional to each other. I

14. In a process of paper manufacture wherein a paper web of pulp and water is continuously formed and advanced, the

herein-described step or steps of controlling the thickness of the web by electric resistanee measurements, which procedure consists of passing an electric current lengthwise through a constant web area and also perpendicularly through said web, whereby said currents will vary as the resistances of their paths through the web vary, and passing said currents through two adjacent respectively. signed and day of May,

WILLIAM P. SOHWEITZER.

In witness whereof I have sealed this'specification this 1st 1930.

web by electric resist- 

